Wireless communication networks and the Internet network are expanding rapidly and their number of users is increasing. The GPRS (General Packet Radio Service) of the GSM (Global System for Mobile Communications) provides means for transferring information in packet switched mode in a cellular radio network. GPRS also provides an interface to other packet switched networks, such as the Internet network.
FIG. 1 shows the interconnections of a telecommunication network in a packet switched GPRS service. The main element of the network's infrastructure for providing GPRS services is a GPRS support node. GPRS support nodes are categorised into Serving GPRS Support Nodes SGSN which, in packet switched data transmission correspond to the Mobile Switching Centers MSC of the GSM network, known in connection with circuit switched data transmission, and Gateway GPRS Support Nodes GGSN. An SGSN is a support node that transmits data packets to a wireless terminal MS (Mobile Station) and receives data packets transmitted by a wireless terminal through a Base Station System BSS, comprising base transceiver stations BTS and base station controllers BSC. In this description, the term wireless terminal MS is used to mean all terminals that communicate over a specific radio interface. Thus, a computer terminal that communicates through a mobile station attached thereto will also be referred to as a wireless terminal. The SGSN also maintains information on the location of the wireless terminals that move in its service area in GPRS registers (not shown in FIG. 1). Physically, the SGSN is typically implemented as a separate network element. The GGSN that communicates with the SGSN provides a connection to and enables co-operation with other networks. Such networks can be, among others, another operator's GPRS (cellular) network or a private network such as, for example, a company's Intranet network, a public switched packet data network PSPDN such as, for example, the Internet network or an X.25 network.
For a long time, the user of a computer terminal in communication with the Internet network has had the opportunity to retrieve multimedia components, such as pictures, text, short video clips and audio clips in electronic format, into his computer terminal from a server of the Internet network. As data transfer rates increase and the properties of mobile stations improve, an interest in a multimedia messaging service and messaging services in general has now also been awakened in wireless networks. As networks that support packet switched data transmission, the GPRS network and 3rd generation mobile communication networks, such as CDMA2000 (Code Division Multiple Access) and WCDMA (Wideband CDMA) in particular, are very well suited for the implementation of a multimedia messaging service.
A multimedia messaging service for 3rd generation mobile communication networks has been proposed which would be implemented in a manner similar to the Short Message Service SMS in a GSM network, i.e. substantially in a store-and-forward manner by transferring messages addressed to a wireless terminal, stored in a specific messaging server, to the wireless terminal when it can be contacted. Said messaging server would preferably be located outside the cellular network in question, for example, in the Internet network.
In the following, a GPRS network will be examined. In the GPRS service of the GSM network, a wireless terminal “attached” to the GPRS network can transmit and receive short messages. The wireless terminal can transmit and receive data in packet switched mode if it is attached to the GPRS network and, in addition, it has an active PDP-context (PDP=Packet Data Protocol) with some GGSN. Activation of a PDP-context may be effected either at the request of the wireless terminal or the network.
It is expedient for the messaging server to make specific inquiries to the GPRS network from time to time. For example, on receiving a message addressed to a given wireless terminal, it is expedient for the messaging server to make sure, by making an inquiry, that the wireless terminal in question is actually ready to receive the message (i.e. it has an active PDP-context with some GGSN), before transmitting the message to the GPRS network . In cellular networks, dynamic PDP addresses (such as dynamic IP addresses, Internet Protocol) are often allocated to terminals. In this case, a wireless terminal does not necessarily always have use of the same PDP address, but when a wireless terminal requests a PDP address, the network gives it a PDP address, which may be the same PDP address the wireless terminal had on a previous occassion, or some other PDP address, depending on what PDP addresses the network has free at that time for the use of wireless terminals.
When using dynamic IP addresses there is a problem associated with performing the previously mentioned inquiry to identify said wireless terminal from outside the cellular network (GPRS network): How can a wireless terminal be identified from outside a cellular network so that inquiries relating to the wireless terminal can also be carried out reliably when the wireless terminal has a dynamic PDP address?